1. Field of the Invention
This invention relates to liquid crystal displays, and more particularly to liquid crystal displays wherein resistance differences caused by electrode link length differences are substantially eliminated.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls light transmissivity using electric fields to display a picture corresponding to video signals. To this end, the LCD includes a liquid crystal display panel having liquid crystal cells arranged in a matrix, and driving circuitry for driving the liquid crystal display panel.
In a liquid crystal display panel, gate lines and data lines are arranged such that they cross each other. The liquid crystal cells are located in the areas defined by the crossing lines. The liquid crystal display panel includes pixel electrodes and a common electrode for applying electric fields to the liquid crystal cells. Each pixel electrode is connected, via source and drain electrodes of a switching thin film transistor, to a data line. The gate electrode of the switching thin film transistor is connected a gate line. By selectively applying appropriate signals to the various data and gate lines, a desired pixel voltage signal can be applied to each pixel electrode.
The driving circuitry includes gate drivers for driving the gate lines, data drivers for driving the data lines, and a common voltage generator for driving the common electrode. The gate drivers sequentially apply scanning signals (or gate signals) to the gate lines, which causes a row of thin film transistors with gates connected to a particular gate line to be driven. The data drivers sequentially apply data voltage signals to data lines, which causes a column of thin film transistors having electrodes connected to a particular data line to be driven. The common voltage generator applies a common voltage signal to the common electrode. Accordingly, the liquid crystal element driven by both a scanning signal and a data voltage signal is enabled. An electric field is then applied between the pixel electrode of that liquid crystal element and the common electrode, causing the light transmissivity to change in accordance with the data voltage signal, causing a pixel to be displayed.
The driving circuitry usually takes the form of chips that are mounted on tape carrier packages (TCP) of a tape automated bonding (TAB) system. The TCPs connect to electrode pads provided on a liquid crystal display panel. The electrode pads in turn connect via electrode links to signal lines at a pixel area. Thus, the driving circuitry electrically connects to the signal lines at a pixel area.
In an LCD, as the number of pixels increase to form a high-resolution picture, the available conductor width and conductor spacing becomes very small. Furthermore, a high integrated density of driving circuits in a PDA (Personal Digital Assistant) employing a small liquid crystal device of below 6 inch enforces the pad spacing to be very small. As a consequence and as shown in FIG. 1, the electrode links between the electrode pads and the signal lines at the pixel area have lengths that vary in accordance with their positions. Since conductor resistance depends on conductor length, the electrode links have resistance that vary in accord with position.
FIG. 1 also shows an electrode arrangement of a gate pad-link portion in a conventional LCD. In FIG. 1, a gate pad 12 connected to a gate driving circuit (not shown) is provided at an edge portion of a lower substrate 10. The gate pad 12 applies a driving signal from the gate driving circuit, via a gate link GK, to a gate line GL that is arranged at a pixel area.
The gate pad 12 has a structure as shown in FIG. 2 and in FIG. 3. The gate pad 12 includes a gate pattern 16 formed on a substrate 26, a gate insulating film 22, and a protective film 24. The gate pattern, gate insulating film, and protective film are sequentially disposed on the substrate 26. An opening in the gate insulating film 22 and protective film 24 exposes a pad area of the gate pattern 16. A transparent electrode pattern 18 is in contact with the exposed gate pattern 16. That transparent electrode pattern 18 is also in electrical contact with the TCP having the driving circuit via a contact portion 20, shown in FIG. 2.
Turning back to FIG. 1, the gate links GK have lengths that depend on their positions, whereas they have the same width and thickness. Accordingly, the resistances of adjacent gate links GK only have a small difference. However, a large resistive difference exists between the ‘A’ portion, where the gate link lengths are relatively small, and the ‘B’ portion, where the gate link lengths are relatively large. As a result, the gate signals applied to the gate lines GL are distorted, causing picture quality deterioration.
Similarly, the data links between the data pads and the data electrodes also have a resistive difference according to the wire length. This resistive difference causes a distortion of the data signals applied to the data lines, which causes picture quality deterioration.
Therefore, a display having little or no differences in the resistances of gate links and/or of data links would be beneficial.